[PATCH] libata: implement ATA printk helpers

Implement ata_{port|dev}_printk() which prefixes the message with
proper identification string.  This change is necessary for later PM
support because devices and links should be identified differently
depending on how they are attached.

This also helps unifying device id strings.  Currently, there are two
forms in use (P is the port number D device number) - 'ataP(D):', and
'ataP: dev D '.  These macros also make it harder to forget proper ID
string (e.g. printing only port number when a device is in question).

Debug message handling can be integrated into these printk macros by
passing debug type and level via @lv.

Signed-off-by: Tejun Heo <htejun@gmail.com>